Engineering Wonders of the World
Volume I

94 ENGINEERING WONDERS OF THE WORLD. The total weight of the bridge is about 1,500 tons. With the full “ live load ” added, and the stresses due to the horizontal thrust of the arch, to temperature, and to wind pressure, each of the four bearings on which the arch rests is called upon to sustain a maximum thrust of some 1,600 tons. The combination of ease of movement at these four points with tai built in six sections of thick steel plates. At the top of the pedestal is a steel forging, in which from end to end is cut a semicircular channel 1 foot in diameter. In the groove rests a huge steel hinge pin—also 1 foot in diameter—5 feet 10 inches long, pierced by a central bolt hole. Pressing on the top of the pin is a second channelled forging, named the TRIAL ERECTION OF THE CENTRE PANEL OF THE ARCH. {Photo, The, Cleveland Bridge Company.) power to resist great pressure was one of the chief problems confronting the designer, and it received a masterly solution. Beginning at the bottom, we find at each point of support a solid foun- dation of concrete, reinforced with steel bars. To this is affixed by four huge bolts, 3 inches in diameter, a massive base plate, carrying an equally massive pedes- The Bearings and Skewbacks. “ saddle,” supporting the skewback, a beam of immense strength, in which meet an end post, the main boom of the arch, and two members of the vertical and lateral bracings. This arrangement allows the saddle of the skewback to move circumferentially on the pin and relieve the varying stresses of the steelwork above. To prevent the pins shift- ing endways, each has an annular projection in the middle, engaging with corresponding